bool 布尔
Table of Contents

布尔值

In [22]: bool(None)
Out[22]: False

In [23]: bool(True)
Out[23]: True

In [24]: bool([])
Out[24]: False

__len__

不存在__bool__ ， 返回结果由__len__ 决定

In [32]: class Test():
    ...:     def __len__(self):
    ...:         return False
    ...:
    ...: print(bool(Test()))
False

In [33]: class Test():
    ...:     def __len__(self):
    ...:         return True
    ...:
    ...: print(bool(Test()))
True

__bool__

In [34]: class Test():
    ...:     def __len__(self):
    ...:         return False
    ...:
    ...:     def __bool__(self):
    ...:         return True
    ...:
    ...: print(bool(Test()))
True